(js-syntax-propertize-regexp): Recognize "slash in a character class"

Fixes: debbugs:19397

* lisp/progmodes/js.el (js--syntax-propertize-regexp-syntax-table): New var.
(js-syntax-propertize-regexp): Use it to recognize "slash in
a character class".
Use a new user option instead of hard-coding shell display.

* lisp/shell.el (shell-display-buffer-actions): New user option.
(shell): Pass it to `pop-to-buffer' instead of hard-coding
`pop-to-buffer-same-window'.